A simple one-pot synthesis of Jacobson-Katsuki type chiral Mn(III)-salen catalyst immobilized in silica by sol-gel process and applications in asymmetric epoxidation of alkenes

Salen ligand synthesized from (1R,2R)-(-)-1,2-diaminocyclohexane and 2-hydroxy-3(3-triethoxysilylpropyl)-benzaldehyde has been used as manganese chelate for the immobilization of the catalytic site. Sol-gel hydrolysis and polycondensation of this chelate with ten equivalents of tetraethyl orthosilicate produced the heterogeneous catalyst. This catalyst is active in enantioselective epoxidations of alkenes in 61-76% yield and 54-86% e.e., using sodium hypochlorite as the primary oxidant. Additionally the immobilized catalyst shows an improvement in the enantioselectivity when compared to the homogeneous Mn(III)-salen analog. (C) 2008 Elsevier B.V. All rights reserved.